The retention and deposition of therapeutic aerosols is dependent on the aerodynamic size of the particle. The aerodynamic size of the particle depends on its physical characteristics and can not be measured by current techniques without knowing these physical characteristics. The heterodispersity of therapeutic aerosols further complicates analysis. The Graduate Institute of Technology at the University of Arkansas has developed a device which can measure particulate concentration and aerodynamic size distribution of an aerosol in situ and in real time independent of the physical properties of the aerosol. This device called the laser Doppler velocimeter particle size analyzer measures the frequency shift of a laser beam reflected by the moving particulate content of an aerosol. In this study, this instrument will be combined with a particle analyzer for measurement of particulate concentration, particulate aerodynamic size distribution, and particulate charge of an aerosol as it is inhaled and exhaled. Therapeutic aerosols will be delivered to the subject in a relatively monodisperse form and also as the heterodisperse aerosol produced by the clinical used aerosol generators. Similar studies will also be made on subjects by sampling through tracheostomy stoma. By sampling at the tracheostomy, information regarding retention of the aerosol above and below that site on inspiration and expiration can be obtained. Using these models the influence of respiratory pattern, particulate charge, and humidity of inspired air on aerosol retention will be evaluated. The final phase of the study will be devoted to the development of a dog model which will allow sampling of inhaled air from peripheral airways and alveoli and analysis of that sample for particulate characteristics by the LDV particle size analyzer. This study will permit the characterization of the aerodynamic size distribution of therapeutic aerosols, their stability, and the influence of humidity on hygroscopicity. Also to be determined are the effects of particulate concentration, size distribution, charge, respiratory pattern, and airway obstruction on total retention and on distribution above and below a tracheostomy stoma.